The invention relates to a disk brake for commercial vehicles, and particularly to a wear-adjusting system for such disk brakes, as well as to a method for controlling such an adjusting system.
Application devices for disk brakes are known, in the case of which a wear adjusting device, which is independent of the brake application, is driven electromechanically.
Thus, distance sensors can, for example, be utilized for adjusting the release play, whose signals are used for controlling the actuating drive of the adjusting device.
However, controls of this type require high expenditures for the sensing and electronic controlling and are also susceptible to disturbances. Systems of this type are described, for example, in European Patent Document EP 0 995 921 A1, in European Patent Document EP 0 995 923 A2 and in International Patent Document PCT/WO 99/08018.
A clearly simpler and, in addition, reliable operating mode of the wear adjusting system operated by means of an electromechanical drive is possible if, when the brake is not operated, the rotating device causes the brake shoes to briefly come in contact with the brake disk and then, starting from this position, restores them by a predetermined amount which corresponds to the desired release play. Such a method of operation is described in German Patent Document DE 197 31 696 A1. Controls of this type have been successful per se. However, with respect to a special operating case, they require further improvements.
If, specifically at the moment at which the adjusting system applies the brakes shoes to the brake disk for adjusting the release play, another braking is initiated and if, in addition, the brake shoes and the brake disk noticeably heat up because of the resulting heat development, as a result of the expansion, the brake may remain applied after the termination of the braking operation such that, because of the frictional resistance occurring as a result of the interaction in the self-lockingly designed adjusting threads between the adjusting nut and the adjusting spindle, the relatively small dimensioned driving motor of the wear adjusting system can no longer turn back the adjusting system. Because of these effects, the release play at the brake cannot be restored. As a result of this effect, the brake will grind during the drive which causes a further high braking temperature and an extremely high wear.
It is therefore an object of the invention to further develop the disk brake of the above-mentioned type such that, with respect to the method and the construction, a reliable release play is ensured in a simple manner.
According to the idea of the invention, it is provided that, in addition to the electric-motor drive, the adjusting system has a release device which promotes the release of the adjusting rotating device.
If, during the operation of the disk brake, an operating situation occurs in which the electric-motor drive, because of the application of the brake, can no longer correctly adjust the release play, the additional release device will promote this release process. As a result of the joint effect of the electric-motor drive and the supplementary release device, the release play remains precisely adjustable despite the application of the brake.
It is one solution to design the release device to be purely mechanical. As an alternative, it is conceivable to use electromechanically or electronically operated systems for supporting the release effect. Piezo elements can, for example, be used here which, when energized, can eliminate the application of the brake.
According to a preferred embodiment of the invention, it is provided that the adjusting rotating device has an adjusting nut into which a rotating spindle is screwed which, on one of its ends, has a thrust piece acting upon the brake pad, in which case the release device acts upon the adjusting nut or the rotating spindle.
This simple constructive implementation of the adjusting rotating device with an adjusting nut and a rotating spindle, which are in each case driven by an electric motor, permits the providing of a separate adjusting rotating device with an electric-motor drive on each side of the disk brake. This can be used, for example, in the case of disk brakes which are constructed as fixed calipers or as a caliper with a very small displacement or swiveling path.
As an alternative, it is conceivable that the adjuster rotating device has a rotating spindle onto which an adjusting nut is screwed which, on one of its ends, has a thrust piece acting on the brake pad, in which case the release device acts upon the adjusting nut or the rotating spindle.
Many different mechanical implementations are conceivable with respect to the release device for an adjusting rotating device with an adjusting nut and rotating spindle.
Expediently, the ramp profile is molded, particularly impressed, directly into the face of the adjusting nut or rotating spindle.
The caliper or an element of the application unit is expediently the supporting element. In this case, an opposite ramp profile can be molded directly into the caliper or the element of the application unit.
Advantageously—since it is easy to manufacture—the ramp profile is molded into a ramp disk which is non-rotatably disposed on the face of the adjusting nut or the rotating spindle.
A particularly cost-effective variant is distinguished in that the release device is constructed in such a manner that the pressure supporting surface of the adjusting nut is equipped with a ramp profile, in which case a supporting disk with an opposite ramp profile rests on the pressure supporting surface, and in which case the flat back side of the supporting disk rests against a supporting surface of a supporting element.
This supporting element may, for example, be the caliper or, on the side of the application device, a brake lever, or an additional force transmission element placed between the brake lever and the rotating spindle or adjusting nut.
The release device is preferably arranged only on the side of the brake situated opposite the application device. For releasing or adjusting the brake release play in the initially described special case of the applied brake, it is sufficient for the brake to be released from its application at least on one side. Because of the supporting of the rotating spindles on the caliper, the corresponding release device can be arranged between the caliper and the thrust piece. Naturally, a variant with a release device on both sides of the brake disk or on the side of the application device is also conceivable.
The invention makes it possible in a simple manner to displace the brake lever and/or the piston unit by a defined amount during each activation of the adjusting system in the direction of the brake disk by means of a mechanism which, also when the brake is applied, can be released again by the adjusting device or releases automatically, after previously the electric-motor actuating drive, with the assistance of the release device, has moved the thrust pieces so far away from the brake disk that, in the event of a possibly unacceptably small brake release play, because of a heating and application of the brake, at least the amount of the desired brake release play is reached.
In this case, the wear adjusting device is operated until the brake shoes have contact with the brake disk. Subsequently, by releasing the brake release play securing mechanism, the desired brake release play is restored in that the brake lever and/or the piston unit are moved by means of the actuating drive or automatically again by the defined amount away from the brake disk.
This method facilitates also the adjusting of the brake release play per se because the desired brake release play is defined by the amount of the advancing stroke of the brake release play securing mechanism or of the release mechanism as a fixed construction characteristic and does not have to be adjusted by an electronically controlled restoring of the adjusting spindles.
As an alternative to the described ramp system, it is also possible to provide a type of clamping roller free wheel or a clamping body free wheel as the release device. These two variants of the release device can also be constructively implemented in a cost-effective manner and can also be mounted particularly compactly between the adjusting nut and the caliper or another supporting element. Thus, it is possible to provide indentations on the face of the adjusting nut or in a ring placed thereon, which indentations receive the clamping bodies. In the case of a clamping roller system, these indentations are preferably ramp-shaped. In the case of a clamping body system, they are preferably constructed parallel to the supporting surface.
According to the method of the invention, first, for adjusting the brake release play by one controlling of the driving motor, a restoring of the rotating adjusting spindles can take place for securing the minimum brake release play. Subsequently, another controlling takes place in the sense of an advancing movement of the adjusting rotating spindles, while simultaneously the advancing movement of the brake release play securing device is triggered. After a sufficiently dimensioned waiting time, which is designed such that the brake shoes can be placed against the brake disk, by means of the actuating drive, a reversely rotating release pulse for securing the brake release play is initiated in order to secure the desired brake release play in this manner. In this manner, a very reliably operating electromechanical wear adjusting device is implemented by very simple means and low sensing and controlling expenditures.
As an alternative to observing a waiting period, the end of the rotating movement of the motor can be determined by a sensing (stop detection), or the stopping point in time of the actuating drive can be determined by means of an excess current sensor.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.